Leiosolenus curtus (Lischke, 1874) was collected from dead shells of Tetraclitajaponica (Pilsbry, 1916) in Manazuru, Kanagawa Prefecture, Japan. It is known that L.curtus bores into limestone, sandstone, and mudstone, however, L. curtus boring into deadshells of T. japonica has not been reported. In this study, the shell form of L. curtus boringinto dead shells was described, and compared with that of the standard L. curtus boring intocalcareous sandstone. The shell size of the former is smaller, and the shell shape is moreinflated and relatively spherical. In the letter, the calcareous encrustation, deposited onthe periostracum, forms vertical folds around the ventral margin, but in dead shell-boring L.curtus , this is smooth. In L. curtus boring into calcareous sandstone, the relative growthequation showed that the shell length grew more rapidly than the shell height, and in L.curtus boring into dead shells, the proportions do not vary regarding shell growth.Leiosolenus has been classified on the basis of the shell form and calcareous encrustation.These two parameters, however, easily change according to the properties of the substratum.Thus, information on the substratum is also necessary for the classification of Leiosolenus.Keywords: Mytilidae, boring bivalves, Leiosolenus curtus, Tetraclita japonica, morphology
